The Role of Standard Solutions: Making your Flame Photometer Accurate

The best equipment in the world is useless without careful calibration. At BWB, we have worked hard to automate the flame photometer calibration process to ensure consistency, reliability, and repeatability.

Our objective is to eliminate, as far as possible, human error by using an internal computerised process that tells the operator when to introduce the various solutions for calibration.

Many existing flame photometers still require the user to stay in the lower concentration ranges - typically 50ppm and below -  and to manually calibrate using a Blank testing solution and a Standard testing solution before reading the results directly from the meter or display. Otherwise, operators must manually plot a calibration curve using the Blank and several Standards, then interpolate the results from the graph. It’s a time‑consuming process with plenty of opportunities for error. .

By automating the process as much as possible through informing the operator when to introduce the various liquids, the calibration curve is graphed automatically, using a Blank and a Standard preparation, or optionally more, to enhance accuracy.

Blanks & Standards

So, what are these Blanks & Standards?  They are the very foundation for ensuring accuracy in Flame Photometer results!

Standard Solutions

Standards are solutions prepared with a single element being tested.  Standard solutions for Sodium might be 5ppm, 10, 25, 50, 70, 85, 100, 120, or any number you desire that covers the expected range of your sample or samples.

Values, sometimes with ranges significantly higher or lower, are used for the other elements, including potassium, lithium, calcium, or barium.  In the latter case of barium, for example, you should not set a high value lower than 300 ppm because of sensitivity issues.  Lower values for barium standard solutions could decrease to as little as 50 for the sake of building the calibration curve, but higher is clearly better for accuracy.

For example, with the barium thought… If you knew values would be in the low range, your test substance could be concentrated through evaporation.  Halving its volume would double the concentration, obviously.  You can therefore easily calculate that something reading 268ppm would really represent 134ppm, but be assured of a much higher accuracy rate in your final results.

Blank Solutions

Blank Solutions, on the other hand, contain all of the constituents of the standard solutions, with the exception of the element that is being tested.  Additionally, if a test sample also contains a quantity of hydrochloric acid, then the Blank Solution should contain the same quantity of HCL as the sample.  This avoids crosstalk, or ionic interference, and keeps the results accurate.

Match the Chemistry

Your samples will seldom be presented in pure, uncontaminated distilled water. Solids may have been ashed in a furnace to release the ions of interest from biological matter, with the remaining organic material typically removed using assorted acids. If you're told a sample contains, for example, 3% nitric acid, your task is to add that same acid to your calibration solutions so they match the sample. This prevents crosstalk and ionic interference, the consequence of a calibration that doesn't match the test sample's basic chemistry, and it's just as important as getting the concentration right.

Making Standards and Blanks

Both of these solutions should be prepared or purchased as Stock Solutions in very high concentrations such as 10,000ppm.  They can be diluted to the necessary PPM when used, but low PPM solutions should not be stored since time causes ionic degradation rendering them inaccurate.

World-wide “Never Flush Drugs” campaigns have had limited success.  It’s hard to impress the importance of returning unneeded drugs to the local chemist/pharmacist for proper disposal when people think “What’s the harm in flushing just three little Valium pills?”  Why is this important?

All Standards and Blanks are prepared with diluents, typically deionized, distilled, or double-distilled (DD) water.  Conventional water supplies are rife with sodium, calcium, and potassium.  However, urban water supplies are often contaminated with barium and lithium from improper disposal of unused medications or industrial substances into the sanitary sewers.  It is vital to use the purest water available for preparing these solutions.

Similarly, diluents should be stored in sealed (non-glass) containers so as not to be contaminated by airborne particles, or experience over-concentration due to the evaporative processes.

Serial Dilutions

Given a Stock Solution of 10,000ppm, a 1,000ppm solution is prepared by placing 10ml of stock in a 100ml volumetric flask, and filling with deionised water (distilled or DD water) to the 100ml mark. Decant this into a container marked 1,000ppm.

Take 10ml of the new 1,000ppm solution, place it in a 100ml volumetric flask, and fill it with deionised water to the 100ml line.  Decant that into a new container marked 100ppm. Repeat the process again to make 10ppm and finally one more time to make 1ppm solution.

It is a simple calculation to create a 50ppm solution, using 5ml of the 1,000ppm solution in the 100ml volumetric flask, or even 50 ml of the 100ppm solution, depending on need.  You are only limited by your ability to perform simple maths, and can get any needed PPM value.

Scales

Industrial labs and medical labs use different measurement scales for their work. Most industrial processes use the ppm scale, but medical facilities use the mol/L or mmol/L (moles or millimoles per litre) scale. You can convert between these using Avogadro's number, which tells us one mol of any substance contains 6.02 x 10^23 particles, though as long as you know the atomic mass of the element you're examining, for example sodium at 22.99 grams per mol, it's quicker to use a converter than calculate it by hand each time.

Are You a Good Lab?

One way a client can be confident they're dealing with a good lab is a simple test: send a batch where ordinary samples are interspersed with several identical samples, and check that all of the identical samples come back with exactly the same result. Programmes such as ISO 9001 exist for exactly this reason, quality is assured because every test and procedure follows a very specific set of rules, applied exactly the same way every time. Consistency like this is what makes a lab a trusted, go-to supplier for its customers.

Low PPM Solutions

Low ppm solutions do not store well and should never be kept beyond overnight, the ions degrade too quickly to maintain accuracy. Solutions at 1,000ppm are safe to store for longer. Feel free to ask one of our experts about the life expectancy of a particular concentration.

The Takeaway

Using Standard Solutions provides reliable, consistent results.  BWB provides your new system with everything you need, right out of the box!  The only thing you need to provide is the fuel—propane, butane, or a commercial mixture combination called Liquid Petroleum Gas or LPG.

Set up is quick and easy, and all the instructions are included.  If you are looking for the cutting edge in flame photometry, and a team that is always ready to support you, look no further than BWB.

Give us a call today!  We would love to help you become the experts that customers rely on every day!